This invention relates to cleaning sheets particularly suitable for removal and entrapment of dust, lint, hair, sand, food crumbs, grass and the like.
The use of nonwoven sheets for dry dust-type cleaning are known in the art. Such sheets typically utilize a composite of fibers where the fibers are bonded via adhesive, entangling or other forces. See, for example, U.S. Pat. No. 3,629,047 and U.S. Pat. No. 5,144,729. To provide a durable wiping sheet, reinforcement means have been combined with the staple fibers in the form of a continuous filament or network structure. See, for example, U.S. Pat. No. 4,808,467, U.S. Pat. No. 3,494,821 and U.S. Pat. No. 4,144,370. Also, to provide a product capable of withstanding the rigors of the wiping process, prior nonwoven sheets have employed strongly bonded fibers via one or more of the forces mentioned above. While durable materials are obtained, such strong bonding may adversely impact the materials"" ability to pick up and retain particulate dirt. In an effort to address this concern, U.S. Pat. No. 5,525,397 to Shizuno et al. describes a cleaning sheet comprising a polymeric network layer and at least one nonwoven layer, wherein the two layers are lightly hydroentangled so as to provide a sheet having a low entanglement coefficient. The resulting sheet is said to provide strength and durability, as well as improved dust collecting performance because the composite fibers are lightly hydroentangled. Sheets having a low entanglement coefficient (i.e., not more than 500 m) are said to offer better cleaning performance because a greater degree of fibers are available for contact with dirt.
While the sheets described in the ""397 patent are alleged to address some of the problems with prior nonwoven cleaning sheets, those sheets appear to be generally of a uniform basis weight, at least on a macroscopic level; and are essentially of a uniform caliper, again on a macroscopic level. That is, ordinary and expected basis weight and caliper fluctuations and variations may occur on a random basis, as a result of fluid pressure differentials during hydroentanglement. However, the structure would not be deemed to comprise discrete regions that differ with regard to basis weight. For example, if on a microscopic level, the basis weight of an interstice between fibers were measured, an apparent basis weight of zero would result when, in fact, unless an aperture in the nonwoven structure was being measured, the basis weight of such region is greater than zero. Such fluctuations and variations are a normal and expected result of the hydroentangling process. The skilled artisan would interpret nonwovens having such variations, including those described in the ""397 patent, as having essentially a uniform basis weight and caliper, in the macroscopic sense. The result of a sheet having a uniform basis weight is that the material is not particularly suitable for collecting and entrapping soil of a diverse size, shape, etc.
As such, there is a continuing need to provide cleaning sheets that offer improved soil removal. In this regard, Applicants have discovered that, surprisingly, by providing regions of high and low basis weight in the cleaning sheet, especially when the sheet is in the form of a nonwoven structure, enhanced soil removal and entrapment are achieved, particularly when soils having various size, shape, consistency, and the like, are encountered. In another respect, Applicants have found that by providing increased three-dimensionality, in the macroscopic sense, to cleaning sheets, enhanced soil removal is achieved.
Accordingly, it is an object of this invention to overcome the problems of the prior art and particularly to provide a structure more capable of removing and entrapping various types of soil. Specifically, it is an object of this invention to provide a nonwoven structure having an essentially continuous high basis weight region and discrete regions of low basis weights, particularly wherein the low basis weight regions are circumscribed by the continuous high basis weight region. It is another object to provide a nonwoven structure having significant three-dimensionality, which will be described in detail below.
It is another object to provide improved processes for cleaning and desirable benefits for the consumer and user of the sheets, especially by packaging the sheets, either in roll form, with perforations for separating sheets, or means for separating the sheets into useful lengths, and packaging them in packages that inform the consumer of the improved processes and/or the benefits that can be obtained, especially those benefits that are not intuitively obvious to the consumer. It is another object to provide cleaning sheets with additives, especially those that improve adherence of soil to the substrate, and especially for those sheets described hereinafter with different basis weights and/or three dimensional structure, such combinations having special performance benefits, and such combinations providing improved benefits.
The present invention relates to a cleaning sheet having at least two regions, where the regions are distinguished by basis weight. In particular, the cleaning sheet comprises one or more high basis weight regions having a basis weight of from about 30 to about 120 g/m2 and one or more low basis weight regions, wherein the low basis weight region(s) have a basis weight that is not more than about 80% of the basis weight of the high basis weight region(s). In one a preferred aspect, the first region is of relatively high basis weight and comprises an essentially continuous network. The second region comprises a plurality of mutually discrete regions of relatively low basis weight and which are circumscribed by the high basis weight first region. In particular, a preferred cleaning sheet comprises a continuous region having a basis weight of from about 30 to about 120 g/m2 and a plurality of discontinuous regions circumscribed by the high basis weight region, wherein the discontinuous regions are disposed in a nonrandom, repeating pattern and have a basis weight of not more than about 80% of the basis weight of the continuous region.
In one embodiment, the cleaning sheet will have, in addition to regions which differ with regard to basis weight, substantial macroscopic three-dimensionality. As used herein, the term xe2x80x9cmacroscopic three-dimensionalityxe2x80x9d, when used to describe three-dimensional cleaning sheets, means the three-dimensional pattern is readily visible to the naked eye when the perpendicular distance between the viewer""s eye and the plane of the sheet is about 12 inches. In other words, the three-dimensional structures of the present invention are cleaning sheets that are non-planar, in that one or both surfaces of the sheet exist in multiple planes, where the distance between those planes is observable to the naked eye when the structure is observed from about 12 inches. By way of contrast, the term xe2x80x9cplanarxe2x80x9d refers to cleaning sheets having fine-scale surface aberrations on one or both sides, the surface aberrations not being readily visible to the naked eye when the perpendicular distance between the viewer""s eye and the plane of the web is about 12 inches or greater. In other words, on a macroscale, the observer would not observe that one or both surfaces of the sheet exist in multiple planes so as to be three-dimensional. The macroscopically three-dimensional structures of the present invention optionally comprise a scrim material, which when heated and then cooled contracts so as to provide a macroscopic three-dimensional structure. Other materials which provide contractile forces so as to provide three-dimensionality are discussed below. Macroscopic three-dimensionality is described herein in terms of xe2x80x9caverage height differentialxe2x80x9d, which is defined herein as the average distance between adjacent peaks and valleys of a given surface of a sheet, as well as the xe2x80x9caverage peak-to-peakxe2x80x9d distance, which is the average distance between adjacent peaks of a given surface. Macroscopic three-dimensionality is also described in terms of the xe2x80x9cSurface Topography Indexxe2x80x9d of the outward surface(s) of the cleaning sheet; Surface Topography Index is the ratio obtained by dividing the Average Height Differential of a surface by the Average Peak to Peak Distance of that surface. In one embodiment, both of the sheet""s outward surfaces will have the described Average Peak to Peak Distance and Surface Topography properties. Methods for measuring Average Peak to Peak Distance and Average Height Differential are described in detail in the Test Method section, below.
The sheets of this invention and similar sheets, especially those that contain additives at low levels, as described herein, and especially those where the additive is substantially uniformly attached over at least one continuous area, can be used in improved processes for cleaning and to provide desirable benefits for the consumer and user of the sheets, some of those benefits being ones that are not intuitively obvious to a consumer, as detailed hereinafter. It is therefore desirable to package the sheets, either in roll form, with perforations for aiding in separating sheets, or with means for separating the sheets into useful lengths, and/or packaging them in packages that inform the consumer of the improved processes and/or the benefits that can be obtained, especially those benefits that are not intuitively obvious to the consumer. The cleaning sheets with additives, including those with desirable low levels of such additives, preferably substantially uniformly attached, at least in one, or more areas, provide, in combination, special performance benefits, and such combinations can provide improved benefits, especially when the sheets have the desirable structures set forth herein.